1. Field of the Invention
This invention concerns liner hangers, methods for hanging a liner casing in a well bore, and methods for manipulating a liner casing during a cementing operation. More specifically, the present invention concerns apparatus and methods for use in rotating a liner casing in a well bore during cementing operations.
2. The Prior Art
In well drilling and completion operations, after the borehole is drilled, a tubular liner casing is positioned in the well bore and the annulus between the liner casing and well bore is filled with cement. The liner casing cementing operations are conducted by running the liner casing in the well bore by means of a setting tool and a drill string or string of tubing where the setting tool interconnects the drill string and the liner casing. The liner hanger (attached to the upper end of the liner casing) is set in the well bore at a desired location so that the weight of the liner casing is supported by the liner hanger. Next, cement is introduced through the drill string and through the liner casing and flows out of the bottom of the liner casing into the annulus between the liner casing and the well bore. After filling the annulus with cement, the setting tool is released from the liner casing and retrieved with the drill string.
The liner casing is set or suspended by a liner hanger at a location in the well bore so that the end of the liner casing extends to close proximity to the bottom of the drilled well bore. At the lower end of the liner casing is a cement shoe with several orifices through which cement is introduced to the annulus between the liner casing and the borehole.
The cement slurry which is introduced to the annulus moves upwardly in the annulus between the liner casing and the well bore. As the cement slurry travels upwardly in the annulus, it displaces the drilling mud in the well bore above the cement.
If the liner casing is reciprocated and/or rotated during the cementing operation, this movement will greatly assist the obtaining of a uniform distribution of the cement in the annulus and proper displacement of the drilling mud in the annulus without channeling of the cement through the mud. In order to rotate the liner casing during the cementing operation, the drill string must be connected to the liner casing and to the liner hanger so that rotation of the drill string causes the liner casing to be rotated relative to the liner hanger until after the cementing operation is complete. Thereafter, the drill string is released from the liner hanger and is pulled out of the well leaving the liner casing cemented in place.
When the liner hanger for the liner casing is set in the well casing, it is set so the bottom of the cement shoe is just above the bottom of the borehole to eliminate the possibility of fouling of the cement shoe orifices and to leave the liner casing pipe hanging under its own weight from the next above well casing. As may be appreciated, the operation requires considerable care because once the cementing is complete, the liner casing pipe cannot be removed and repositioned since the cement is already in place. Also, if the releasing mechanism in the liner hanger fails to disengage from the drill string prior to the cement hardening up, the drill string could also be cemented in place. Such malfunctions can result in the loss of well equipment in the well or even destroying the well. Also, if the drill string is released from the liner casing prior to pumping cement, then reciprocation or rotation of the liner casing during the cementing operations is not possible since the drill string must be attached to the liner casing pipe to move it. Thus, the advantages of reciprocating and rotating of the liner casing pipe during the cementing operation are lost.
It has been proposed to incorporate in a liner hanger, a rotatable bearing between horizontal load bearing surfaces in the liner hanger so that when the liner hanger is set and the liner casing suspended from the next above string of well pipe, the liner casing is supported in the liner hanger on a rotational bearing. The rotational bearing then facilitates rotation of the liner casing relative to the liner hanger after setting the liner hanger. However, in many wells, the weight of the suspended liner casing subjects the rotational bearing to excess stress and the bearing wears out rapidly. Also, exposure of the bearing to the well bore environment also causes excessive wear of the bearing. If the bearing malfunctions, then the casing liner may not be rotated during cementing. It is virtually impossible for the operator at the surface to have any qualitative indication of the downhole operations.
Examples of rotatable load bearing bearings and liner hangers are shown in U.S. Pat. No. 4,033,640 and U.S. Pat. No. 4,190,300.
Despite use of rotatable bearings in liner hangers, the torque required to rotate a liner in a borehole often has been excessive to the point of twisting off or breaking the pipe downhole. At the earth's surface, it is difficult for the operator to determine whether this excessive drag in the borehole is a result of poor operation of the rotatable bearing or simply high pipe friction in the well bore due to a crooked or tight hole. A third source of excessive drag in the borehole is the result of high contact forces between the contacting surfaces of the stationary slip cone member and the liner hanger mandrel which is in rotating contact with the slip cone member.
The present invention provides a unique system for the operator to determine downhole drag characteristics prior to cementing, either before and/or after the liner is suspended. The invention further provides an apparatus that minimizes frictional drag associated with the high contact loading between the contacting surfaces of the cone and liner hanger body.